1. Field of the Invention
The present invention relates to an apparatus and method for mixed signal spread spectrum receiving. More particularly, the present invention relates to an apparatus and method for providing mixed signal spread spectrum receiving using spectrum aggregation.
2. Description of the Related Art
Mobile terminals are used to provide wireless communication services to users. As wireless communication technology has advanced, mobile terminals may provide a variety of functions in addition to simple telephone conversation and/or voice services. For example, mobile terminals may provide functions such as an alarm, a Short Messaging Service (SMS), a Multimedia Message Service (MMS), E-mail, games, remote control of short range communication, Near Field Communication (NFC) and/or other short range communication services, an image and/or video capturing function using a mounted camera, a multimedia function for providing, viewing and/or generating audio and video content, a scheduling function, and many more similar functions and/or functions suitable for being provided on mobile terminals. With the plurality of features provided, mobile terminals are increasingly used by a greater number of users and, concurrently, use a greater amount of bandwidth of wireless communications networks.
In order to accommodate the greater number of users, advances in wireless communication technology maximize spectrum usage according to various techniques, such as spectrum aggregation. Spectrum aggregation allows for simultaneous use of non-contiguous parts of a wireless spectrum from various bands of the wireless spectrum. Spectrum aggregation allows for transmission of a large throughput signal that may not be transmittable using contiguous parts of the wireless spectrum. Another technique for maximizing spectrum usage is to perform higher order modulation so that each transmitted symbol communicates a larger number of bits than a symbol transmitted according to a lower order modulation.
However, in order to provide higher order modulation, a Signal-to-Noise Ratio (SNR) of a wireless channel must be at an appropriate level, i.e., sufficiently high, to support decoding requirements of the higher order modulation. Wireless communications systems using Multi-Input Multi-Output (MIMO) architecture for transmitters, receivers and/or transceivers that use multiple parallel receiver chains may improve an effective SNR of a wireless channel. Use of higher numbers of receivers in the multiple parallel receiver chains allows for larger SNR improvements such that when the wireless channel has a good SNR, the multiple parallel receivers may be used to concatenate bit streams in order to further increase throughput for the transmitted signal. However, when the above discussed technologies are applied to MIMO receivers using the multiple parallel receivers, an amount of silicon used and a package size for receiver chips may increase, and accordingly, an amount of power consumed by the receiver chips may also increase. The increase in power consumption of the receiver chips may cause a decrease in battery life of mobile terminals and, thus, may cause an inconvenience to the user.
In a MIMO architecture having multiple parallel receiver chains, the number of parallel receiver chains may correspond to a number of MIMO inputs/outputs or may correspond to a number of non-contiguous parts of the spectrum that are to be aggregated. In the case of MIMO receivers, each of the receivers should receive the signal and independently process the received signal so as to yield, at a decoder, different content, such as spatial codes and/or data to be concatenated, carried by the signal at respective parts of the signal. In order to perform spectrum aggregation, each part of the spectrum, at various frequency ranges of the spectrum, should be down converted and processed. Because each part of the spectrum should be kept separate, a MIMO receiver that is only analog may down convert to different frequency offsets that are paced adjacent to each other for digital processing.
However, such an implementation of multiple parallel receiver chains for MIMO receivers uses a large amount or size of receiver chips and a large amount of power, and thus, is impractical for MIMO architectures using increasing numbers of MIMO receivers. Additionally, the multiple parallel receiver chain technique may also complicate compensation of characteristics and/or features, such as equalization across bandwidth, absolute gain, In-phase Quadrature (IQ) mismatches, and any other similar characteristics and/or features because each receiver of the multiple parallel receiver chain will have its own Process-Voltage-Temperature (PVT) variation characteristics such that each receiver should be compensated according to its own PVT variation characteristics. Additionally, the multiple parallel receiver chain technique, as described above, produces an additional burden on digital baseband operations due to having to control a large number of analog receivers. Accordingly, there is a need for mixed signal spread spectrum receiving in order to provide a more efficient MIMO receiver and to support higher order modulation in a mobile terminal.